The following statements are made about the killing of virus-infected respiratory epithelial cells by cytotoxic T cells:

A. Priming of the T cells has taken place in the thymus, lymph node, or spleen.
B. Viral antigens have been presented on infected epithelial cells.
C. MHC-I molecules have been presented on infected epithelial cells.
D. MHC-II molecules have been presented on infected epithelial cells.

Which one of the following options represents the combination of all correct statements?

Correct option is A

Explanation:

• Statement A: Priming of the T cells has taken place in the thymus, lymph node, or spleen.

  • This is incorrect in this context because the killing of virus-infected cells by cytotoxic T cells happens after priming, which typically occurs in the lymph nodes or spleen but is not directly involved in the process of killing, which is the focus of this question. The statement does not directly apply to the killing mechanism by cytotoxic T cells.

• Statement B: Viral antigens have been presented on infected epithelial cells.

  • This is correct. Virus-infected epithelial cells present viral antigens on their surface, which is necessary for the cytotoxic T cells to recognize and kill the infected cells. The presence of these viral antigens is what triggers the T cell response.

• Statement C: MHC-I molecules have been presented on infected epithelial cells.

  • This is correct. Infected epithelial cells present viral peptides on MHC-I molecules, which is crucial for recognition by cytotoxic T cells (CD8+ T cells). This allows the cytotoxic T cells to recognize and kill infected cells.

• Statement D: MHC-II molecules have been presented on infected epithelial cells.

  • This is incorrect. MHC-II molecules are typically involved in presenting antigens to helper T cells (CD4+ T cells), not to cytotoxic T cells (CD8+ T cells). MHC-II molecules are generally not expressed by infected epithelial cells for the purpose of activating cytotoxic T cells.

Conclusion:

The correct combination of statements is B and C, as these statements accurately describe the process of cytotoxic T cell killing of virus-infected epithelial cells.

Information Booster:

1. Viral antigens are presented on the surface of infected epithelial cells for recognition by cytotoxic T cells.
2. MHC-I molecules on infected cells present viral peptides, which is essential for the activation of CD8+ T cells.
3. MHC-II molecules are not involved in the presentation of antigens for cytotoxic T cells in this context.
4. The killing process by cytotoxic T cells requires antigen presentation by MHC-I, not MHC-II.